The subject invention concerns a positioning apparatus comprising an elongate housing in which is rotatably mounted a threaded spindle which extends lengthwise inside the housing and on which is mounted a runner engaging the threads of the spindle. The runner is provided with a member projecting in the transverse direction of the positioning apparatus and is arranged, upon rotation of the spindle to travel backwards and forwards in the housing along guides extending around and in parallel with the spindle.
Positioning apparatuses are known wherein an electric motor serves to turn the spindle, preferably via gear mechanism. The spindle may be in the form of a ball bearing screw engaging a nut sleeve of a special design comprising balls. The nut sleeve is connected with a tube known as a positioning tube projecting past the stand in the lengthwise direction thereof, the free end of said positioning tube supporting e.g. an articulated head or a yoke bracket by means of which articles to be displaced backwards and forwards to predetermined positions are secured to the apparatus.
Positioning apparatuses of this kind are useful in that they operate with great precision and with a high degree of efficiency. However, their use is restricted in that the positioning tube including the attachment means of the latter are but a prolongation of the stand.
Furthermore, cylinders comprising a double-acting pneumatic piston-and-cylinder unit are used, the piston of which supports a guide member extending transversely through the cylinder wall and participating in the piston movements, in addition to which this guide member serves as an attachment to support the articles to be moved. This apparatus is more versatile owing to its construction but nevertheless it suffers from certain drawbacks. Its efficiency, for instance, is considerably reduced compared with that of the positioning apparatus described initially and the pneumatic operation prevents movements to the various set positions with the same degree of precision.